As well-known to those skilled in the art, hydrocarbon polymers have been employed for modifying the performance properties of petroleum distillates. The viscosities of petroleum distillates particular lubricating oils vary with temperatures and since performance criteria today demand ever broader temperature ranges for use, additives are incorporated into the lubricating oil to control (the viscosity-temperature relationship). This viscosity-temperature relationship of an oil is known as its viscosity index (VI). The higher the viscosity index, the less the change in viscosity with temperature. Therefore, an ideal viscosity index improver (VIl) would exhibit a negligible viscosity contribution to the lubricating oil at low temperature while providing a large viscosity contribution at temperatures of engine operation.
Traditionally, essentially linear olefin copolymers, particular ethylene-propylene copolymers (referred to as OCP's) have been employed in lubricating oils as viscosity index improvers, pour depressants, dispersants. See generally U.S. Pat. Nos. 3,522,180; 3,524,732; 3,879,304; 4,026,809; 4,089,794; 4,137,185; 4,146,489; 4,171,273; 4,320,019; 4,340,689; 4,357,250; 4,382,007; 4,500,440; 4,640,788; 4,699,723; 4,71 5,975; 4,732,942; 4,764,304; 4,812,261; 4,816,172; 4,820,776; 4,842,756.
The OCP's have the ability to provide a high thickening contribution to the lubricating oil composition thus increasing the viscosity index of the overall composition. Thickening power is generally defined as the difference in the kinematic viscosity of a dilute solution of an OCP mixed with oil and the diluent oil. For example, an oil solution containing from 1 to 2 percent of an OCP which provides a thickening power of 6 to 7 centistokes measured at 100.degree. C. generally indicates acceptable viscosity index improvement performance.
Within a class of structural similar polymers, the higher the molecular weight, the greater the viscosity it imparts to the lubricating oil. However, higher molecular weight polymers exhibit a greater tendency to breakdown under the shear and high temperature conditions normal in engine operation. This, of course, results in a loss in viscosity and the polymers are referred to as lacking in shear stability. Thus, a balance must be achieved between the thickening contribution of the polymer and its tendency to degrade. This shear stability is typically measured as a percent viscosity breakdown on shear under a standard set of conditions. A value below 30 percent viscosity breakdown in a polymer is shear stable as that term is understood in the art.
The composition of the linear ethylene-propylene copolymers can be adjusted so that an excellent balance can be achieved between thickening power and mechanical shear stability, however these compositions tend to have higher than desirable viscosity at very low temperatures. This is related to the ease of engine cranking during start-up in cold climates. The viscosity at low temperature of a lubricating oil composition is defined by the Cold Cranking Simulator (CCS) test, a viscosity under shear at generally -25.degree. C. is measured. To achieve maximum performance under the CCS test blends of OCP's have been employed. See U.S. Pat. Nos. 3,697,429; 4,507,515; 5,391,617; and 5,451,630.
Hydrogenated star branched polymers have been proposed for improving the low temperature rheological properties of lubricating oil compositions. See U.S. Pat. Nos. 4,116,917; 4,141,847; 4,788,361; 4,557,849; 4,849,481; 4,156,673. These hydrogenated star polymers are prepared in the coupling of polymers from the anionic solution polymerization of conjugated dienes, which may optionally also contain monomeric units of a monoalkenyl aromatic hydrocarbon (vinylarenes), with a polyalkenyl coupling agent followed by hydrogenation.
These star polymers of dienes and optionally vinyl arenes have also been functionalized to enhance not only rheological properties of the diluent oil but other desirable multi-functional performance criteria such as disperancy and improved shear stability of the lubricating oil. Functionalization has been effected by direct copolymerization of a functional vinyl monomer followed sometimes by secondary chemical reactions, with for examples amines to obtain dispersant properties, carboxylation via metalization reaction with alkyl lithiums, and free radical grafting. See for example U.S. Pat. Nos. 4,141,847; 4,358,565; 4,409,120; 4,427,834; 4,868,245; 5,141,996; 5,147,570.
While star branched polymers of this type have excellent low temperature performance in lubricating oils, their application has been limited due to their high cost of manufacture. In addition, difficulty has been encountered in derivatizing these star polymers via the well-established techniques of grafting and amination known in the art.
In U.S. Pat. No. 5,030,695 there is purportedly described a technique for producing polyolefin star polymers. In one example, there is described nodular ethylene propylene copolymers in which ethylene, propylene and norbornadiene are copolymerized to form a nodular branched structure to which additional monomers are added to lengthen the nodular arms. Methylacrylate is then added to cap the arms. Another example purports to describe the reaction of a hydroxy terminated ethylene propylene copolymer which is then dissolved in a dry lubricating oil and reacted with a polyfunctional isocyanate (Desmodur R has three isocyanate groups per molecule). Neither reaction conditions of any kind nor any structural characterizations of the polymer are provided.
Hydrocarbon polymers, particularly polyisobutylenes, have been used recently in derivatized form to modify properties of fuels. A problem common to carburetors, the intake system of gasoline engines, and the injection systems for fuel metering in gasoline and diesel engines is contamination by impurities due to dust particles in the air, uncombusted hydrocarbon residues from the combustion chamber and crankcase vent gases passed into the carburetor. Intake deposits interfere with operation of the valves, such as closing, motion and sealing leading to sticking and eventually valve burning. These residues shift the air/fuel ratio during idling and in the lower part-load range so that the mixture becomes richer and the combustion more incomplete and in turn the proportions of uncombusted or partially combusted hydrocarbons in the exhaust gas becomes larger and the gasoline consumption increases.
Fuel additives which overcome these disadvantages are referred to as detergents. Generally, these are low molecular weight hydrocarbon polymers derivatized with polar groups. Typically detergents have been based on aliphatic hydrocarbylamines, particularly polyisobutylamines (see for example U.S. Pat. Nos. 3,438,757; 3,565,804; 3,574,576; 3,848,056; 3,960,515; 4,832,702; 4,173,456; 4,357,148; 4,877,416). While the simple polyisobutylamines have been successful in keeping valves and carburetors clean, they have shown little benefit as sludge dispersing agents. It is well-known in the art of lubricating oil additives that polyamine derivatives of hydrocarbon polymers particularly ethylene-propylene copolymer have excellent dispersant properties.
It is an object of the invention to provide fuel and lubricating oil additive compositions in the form of branched polyolefin polymers in which it is possible to control the composition of the branched polymer by controlling the degree of branching or number of arms coupled to the polymer backbone independent of control of the composition and molecular weight of the arms.
It is also an object of this invention to provide fuel additives in the form of polyolefin branched polymers derivatized with polyamines which function as detergent, dispersant additives.
Thus, there is further realized a need for low cost branched polymeric additives which provide a good balance of thickening efficiency and mechanical shear stability while affording a minimal low temperature viscosity to the lubricating oil composition.
It is a further object of this invention to provide a branched polyolefin polymer which can be functionalized using techniques known in the art.